1. Field of the Invention
The present invention relates to a multi-stage collector for transit-time tubes and in particular traveling wave tubes.
2. The Prior Art
Electron beam catchers are known for transit-time tubes and in particular traveling wave tubes which consist of a plurality of electrodes lying one behind each other in the direction of the beam, the electrodes being maintained at different electrical potentials and adapted to absorb the beam. Such an arrangement is known in the German published Auslegeschrift No. 1,273,703. Such a catcher consists, for example, of a pot-shaped collector electrode and two circular electrodes which are connected together by material which is electrically resistive. The pot-shaped electrode has a catcher plate which is aligned with the electron beam. Electrons which are not deflected to the circular collector electrodes are collected by the catcher plate.
In such a tube, the catcher plate must be able to absorb the heat produced by the energy of the impinging electron beam and dissipate it. It must also be formed so that secondary electrons released when the electron beam strikes the catcher plate are prevented from entering the discharge chamber. The electrical potential of the catcher plate is typically chosen at a value below that of the operating potential of the system components of the amplifying section of the tube such as a delay line, in order to reduce the power loss at the catcher plate. Such an arrangement is illustrated in German Pat. No. 1,221,364.
In the past, a metal point projecting into the collector as a whole and axially aligned with the beam has been used in the last collector stage, and the point is maintained at cathode potential in order to deflect the electrons of the beam away from the axis. This arrangement produces the problem, however, that electrons which are reflected at the tip itself move back into the interaction space and sometimes even travel as far as the cathode, causing a degradation in the high frequency performance of the tube.